Conventionally, autopilot devices which automatically perform steering of ships according to settings have been known. Such an autopilot device can cause a ship concerned to travel on a target course by controlling its rudder based on a difference (variation angle) between the target course and a heading of the ship obtained by a heading sensor. JP1995-242199A, JP2005-178434A, and JP2012-179968A disclose arts relating to such autopilot devices.
JP1995-242199A discloses a method of controlling a rudder by an autopilot device when changing a target course. JP2005-178434A discloses an autopilot device that causes a ship to travel in a circle by gradually changing a target course. JP2012-179968A discloses an autopilot device that stably performs a course control by controlling a rudder according to a wind direction.
Since the autopilot device automatically controls the rudder based on the difference between the target course and the heading, while the ship turns, an operator cannot grasp when the ship concerned stops turning. Unlike an automobile, it generally takes time for a ship to turn and the ship generally rocks while turning. Therefore, the operator desires to grasp the progress of the turn. In this regard, JP1995-242199A, JP2005-178434A, and JP2012-179968A do not disclose anything about notifying the progress of the turn while the ship turns.
Moreover, conventionally, there has been a case where a course after turning and a current heading are displayed simultaneously on the autopilot device, a general-purpose display, etc. Hereinafter, such a case is described with reference to FIGS. 8A and 8B. FIG. 8A is a display screen before the turn. A mode display section 71, a target course display section 72, a heading display section 73, and a rudder angle display section 74 are displayed on the display screen.
In the mode display section 71, “Auto” is displayed during normal autopilot, and “180T” is displayed when turning by a large degree according to a change of the target course. In the target course display section 72, the target course is displayed as a number. In the heading display section 73, the current heading is displayed as a number. In the rudder angle display section 74, the rudder angle and the direction are displayed by using numbers and a scale bar.
FIG. 8B is a display screen while turning. With reference to FIG. 8B, the target course is 169 degrees and the current heading is 303 degrees. Therefore, by calculating difference therebetween, an angle by which the ship has left to turn can be roughly grasped.
However, the heading obviously changes while the ship turns, and therefore, the number in the heading display section 73 rapidly changes. Therefore, the operator needs to read the number changing rapidly and then calculate the difference between the number and the target course, otherwise he/she cannot grasp how much more the ship has left to turn. Besides, especially since the ship rocks while turning, it is not realistic to perform those operations.